Method of treating hydrocarbon distillates



' alkaline solution containng lead oxide, the

j group.

Patented Nov. 21, 1939 artists 2,18 3 PATENT .OFFICE'YI METHOD OFTREATING HYDBOCABBON DISTILLATES Virden w. Wilson, Buffalo, N. r.,assignor to Buffalo Electro-Qhemical Company, Inc., Buffalo,

No Drawing. Application February Serial No. 123.481

10 Claims. (c1. res-2s) This invention relates to the treatment ofhydrocarbon distillates andmore particularly to a mode of procedurewhereby sour distillates are sweetened. I

.A hydrocarbon distillate obtainedby the distillation frompetroleum issourf when upon treatment wtih an alkaline solution containing dissolvedlead oxide, as, for instance, lead oxide,

dissolved in caustic soda, and elementary sulfur, a discoloration isproduced at the interface of the gasoline and the aqueous solution. Thistest is generally designated as the doctor. test; the

doctor solution. A positive doctor test indicates that the distillatescontain sulfur compounds, wherein the group SH is combined with anorganic radical R or hydrogen.

As substantially all hydrocarbon distillates are sold according to rigidspecification requiring that they be sweet, 1. e., show a negativedoctor test, therefore, all distillates containing SH must be treated insome fashion to eliminate this Heretcfore, the method generally employedfor sweetening sour distiilates comprised reacting the undesirablesulfur compounds of the type containing the SH group with a reagentobtained by dissolving lead oxide in caustic alkali, sodium plumbite andthereafter adding elementary sulfur. By this procedure RSH compounds arechanged to innocuous di-sulfldes remaining in the distillate, or areremoved from the distillate. In general, this sweetening procedure maybeillustrated by the following chemical equation It is generallyrecognized that the plumbite or doctor procedure is effective forsweetening gasoline or other sour distillates but suffers thedisadvantage that the procedure is expensive and secondly, that it isnecessary to add elementary sulfur in exact predetermined amounts inaccordance withEquation 2 to prevent the addition of excess free sulfurwhich would produce a corrosive gasoline.

An object of the present invention, therefore, is the provision of amode for sweetening sour petroleum distillates without the necessity ofusing sulfur with the production of a distillate showing a negativedoctor test. Another object .01 the invention is toprovide a method forsweetening sour distillates that is relatively more ecobut not sovigorous as to attack unsaturated compounds present in the distillate..qThus, an alcoholic caustic solution substantially free of water ispreferably employed in the procedure of the present invention, thealkali being either caustic soda or caustic potash; dissolved insubstantially anhydrous alcohol, as, for instance, methyl alcohol, ethylalcohol, propyl alcohol, or other water soluble alcohol. Theconcentration ofcaustic hydroxide dissolved in the alcohol may be anyquantity consistent with the solubility of' the caustic therein,although, in general, solutions of from about one-half normal to abouttwo normal will be found to be practical for the procedure. Thealcoholic caustic and the oxidizing agent may be added to the distillateconcurrently or consecutively.

It is believed that upon the addition of the alcoholic caustic solutionto the gasoline, any mercaptans contained in the gasoline are changed bythe caustic alkali to meroaptides, the mercaptides being changed todlsulfides upon reaction with the oxidizing agent.

In the-practical operation 0' he procedureit has been found preferableto u.-.e an amount of alcoholic caustic substantially in excess of thattheoretically required for the content of me'rcaptans in the distillate'to be sweetened, since the time of contact required to obtain completeconversion of the mercaptan is considerably reduced and is broughtwithin practical operating limits. In general, two and a half to fivefold excess of alcoholic caustic above that required by the mercaptanpresent in the gasoline has been found satisfactory. Representativeresults are outlined in Table 1 below where 100 cc.s of a crude gasolinecontaining 0.078% sulfur as mercaptan was agitated during a given timeperiod of 10 minutes with the indicated normal caustic soda dissolved insubstantially absolute methyl alcohol and the theoretical quantity of100 volume hydrogen peroxide to oxidize the mercaptan sulfur.

Table I Percent of mercaptan Oc.'s ci-normal alcoholic caustic sum comverted Percent It will be noted that 2 cab of normal caustic sodarepresent approximately the theoretical quantity of caustic alkalirequired to exactlyreact with the amount of mercaptan present in thesample of gasoline and that within the given time limit a two andone-half fold excess of caustic alkali permits a substantially completeremoval of the mercaptan sulfur.

In general, the alcohol used in making the alcoholic caustic. should besubstantially anhydrous and contain less than about of water.

As is well known, the more acidic mercaptans, as, for instance, methyland ethyl mercaptan and also hydrogen sulfide are readily removed bycaustic wash and so are not troublesome in practice. In Table II is setforth the results of an investigation upon sweetening of a hydrocarbondistillate made sour by the addition thereto of specified mercaptanssuch as propyl, butyl, amyl and heptyl mercaptans. The sour distillatewas treated with specified alcoholic alkali hydroxide solutions normalin strength and agitated minutes .and- 30 minutes in the presence of aslightexcess of hydrogen peroxide over that required for the conversionof -di-' sulfide.

The mode of-treatment on the experimental work was as follows: 100 cc.of the gasoline under test were pipetted into a clean glass bottle and10 cc. of the caustic treating reagent were added. Immediatelythereafter 0.2 cc. of 100 volume hydrogen peroxide was added. The

bottle was stoppered with a clean new cork stopper and was shaken forthe appropriate length of time. In the conclusion of'this period ofagitation the. bottle was removed and an amount of distilled waterequivalent to the amount of alcohol originally added was pipetted "upperof which was decanted, filteredtoremove small amounts of still suspendedalcohol and water and was then analyzed for mercaptan content, totalsulfur, change inspecific gravity and other items of interest.' In thetablemethyl and ethyl alcohols are abbreviated in the usual way i'asMeOH and EtOH respectively. p I

Table II Percent Percent of Percent Percent of of sulfur $capt-n ofsulfur memptan I8 merl1! conll mer- 811 oon- 9" ca ten vested in cartonvested in tin 10min. letln 30min. solution contact solution contact'PRorYL MEROAPTAN on an 0100111000.-.. 0.1001 0.1001

Me 11400011---." 0.000 100 0.000 100 00 Ei0H-Na0H-' 00100 88.6 0000201.0 00 Eton-K011"; I 0.000 100 M00 100 se sion-noun 0.00 100 0.000 100turn. MERCAPTAN M0 n-Nson 11000 100 0.000 100 00% EtOH-NaOH... 0. 021201.1 0.0100 00.1 canton-noun" 0.000 100 0.000 100 AMYL MEROAPTAN.

i 0.1020 01020 in H-NeO 0. 000. 100 0.000 100 00% EtOH-NaOH.-- 0. 0001 n2 0. 0214 70. 0 as. Et0H- KOH-..- 0. 000 100 0. 000 100 Harm. MEROAPTAII11101. 0 1000 0.1000 MeOE-NaOH 0000 100 0.000 100 00% mon-xom. 0.000 1000.000 100 at. EtOH-NaOH..- 0 0201 7a 1 0.0000 92. 0 abs'ston-xon..;; 0.000 100 0 000 100 In Table m is set forth the results of aninvestigation of the effect of aqueous caustic soda upon various highermercaptans dissolved in gasoline, 100 cc.s of the artificially souredgasoline being agitated with 10 cc.s of normal caustic for the timeindicatedand the residual sulfur determined. The percent sulfur asmercaptan.

in the original samples was approximately 0.1%.

The mode of treatment contemplated in a plant process based on thisexperimentaleviden'ce would be as follows: Sour cracked gasoline whichhad been stabilized for the removal of most of the butane and all of thehydrogen sulfide is first contacted with a -=25 Be. solution of causticsoda. This may be obtained in part at least from the recovery still formethanol to be mentioned subsequently. The aqueous caustic treatmentwill remove the more acidic mercaptans andsucceed in lowering the sulfurcontent of the gasoline by the amount of low molecular weight mercaptanremoved. The caustic washed gasoline is then pumped through a mixingpump into a pipe coil. At the mixing pump a mode-- termined amount ofalcoholic caustic containing suflicient potassium or sodium hydroxide toreact with all the mercaptans present in the gasoline is added andfanamount of concentrated hydrogen peroxide 's uiilcient to insuresweetening is added at the same time. It has been found that betterresults be obtained by such concurrent for recirculation throu8htheprocess. The gasoline is then passed into a washer where it is contactedwith a vigorous scrubbing spray oi! water, the volume of water beingkept as low as possible, yet sufiicient employed to insure completeremoval and separation of the aqueous alcoholic layer from the gasoline.The concentration ofthe alcohol in this layer will be 30-50%.

Buch treatment should leave less than one-half of 1% of the alcoholemployed in the, gasoline.

Thisamount of loss willnot appreciably aifect treating costs since thevolume of alcohol employed will be in the neighborhood of 5-7% of thevolume of the gasoline treated. "The sweetened water-washed gasoline canthen be passed directly to storage while the alcohol extracted by thefinal water wash would be returned to a free-- tionating column, theheat from which could be supplied by exchangers in connection with thecracking still column condenser. The'overhead from the alcoholfractionating column would be,

condensed in the second set oi heat exchangers to eilect maximum heatrecovery and the recovered methanol run to storage, thence to. mixingtanks where iresh alcoholic caustic would be added in quantitiessufllclent to insure adequate caustic present in the gasoline at alltimes. The process of treating and alcohol recovery can thereby be madecyclic and the amount of alcohol required ior'continuous operation willremain substantially constant and need be replaced only tor slightlosses dueto carry-over in the gasoline or to such losses as may occurin tractionation.

From the foregoing it will be seen that the present invention provides amethod for sweetening sour hydrocarbon distillate by the use of asubstantially water free solution of caustic alkali in conjunction withan oxidizing agent capable of changing mercaptides to disulfldes, butnot attacking unsaturated compounds in the gasoline, that is to say, thepercompounds, which are materials capable oigenerating hydrogen peroxidein solution.

What is claimed is:

1. The method or sweetening sour hydrocarbon liquid distillates whichcomprises treating the distillate with an alcoholic solution of causticaikali and an oxidizing agent yielding hydrogen peroxide.

2. The method of sweetening sour hydrocarbon distillates which comprisestreating the liquid distillate with substantially water free alcoholiccaustic alkali and an oxidizing agent capable of yielding hydrogenperoxid 3. The method of sweetening sour hydrocarbon distillates whichcomprises adding alcoholic caustic alkali to the liquid distillate andthen treating the mixture with an oxidizing agent capable of yieldinghydrogen peroxide. 4. The method of sweetening sour hydrocarbondistillates which comprises agitating the liquid distillate withalcoholic caustic alkali and an exidizing agent capable of yieldinghydrogen peroxide and capable of oxidizing mercaptides to disulphides.

5. The method of sweetening so'ur hydrocarbon distillates whichcomprises treating, the liquid distillate with an amount of alcoholiccaustic alkali having sufllcient caustic content to change themercaptans in the sour distillate to mercaptides and treating themixture with suflicient of suillcienthydrogen peroxide to render thedistillate negative to the doctor test.

'7. The method of sweetening sour hydrocarbon distillates whichcomprises treating the liquid distillate with an amount of alcoholiccaustic a1- kali having sufficient caustic content to change themercaptans in the sour distillate to mercaptides and treating themixture with sufiicient of an oxidizing agent capable oi yieldinghydrogen peroxide to change the mercaptans to disulfldes and regeneratethe alkali.

8. The method of sweetening sour hydrocarbon distillates which comprisestreating the liquid distillate with 4-8% 01 an alcoholic caustic alkali,the alcohol being substantially anhydrous methanol, having a causticcontent in excess of the amount required to react with the mercaptans inthe distillate and adding thereto at the same time suflicient hydrogenperoxide to render the distillate negative to the doctor test.

'9. The method of sweetening sour hydrocarbon distillates whichcomprises treating the liquid distillate concurrently with 44% 01' amethanol solution of caustic alkali, having a caustic content sufiicientto react with all the mercaptans present in the distillate and asufllcient quantity of hydrogen peroxide to render the distillatenegative to the doctor test with subsequent removal of theexcess'alcohol by water washing.

10. The method of sweetening sour hydrocarbon distillates whichcomprises adding to the liquid distillate an alcoholic caustic alkalisolution, the alcohol being chosen from the water sol-' uble monohydrlcalcohols in substantial anhydrous condition, and concurrently treatingthe solution so obtained with an oxidizing agent capable oi yieldinghydrogen peroxide.

VIRDEN W. WILSON.

CERTIFICATE 0F CORRECTION.' Patent No. 2,181,056. Novembr 21,- 19 9.

' YI RDE N w.- wI soNJ" .It is hereby certified. that prrorappeai'fa inthe printed. specification of the above mmbered patent zjequiringcorictioi; as follows: Page 2, first column, 1ine'l8,.f9r the aord-"of"-after "converaibn nqad to} page-5, first column, lin'e 26, claim1,- ;trikdut "liquid? and insert the same before "ditil late' in lifie27, same claim; andthgt the said Letters Patent should be read thiscorrection thereiti that the same may corifom to the rec'ord of the case111th; Patent @3190. I v v Signed and. sealed thiq 26th day of December;A.- D. .1959.

Henry Van Arsdle} (Sel) a 4 Acting onnnissioner 'bffatents.

